Which is the actual SD card?

I'm trying to move some videos over to my SD card but there's 2 extensions for the SD card. Sdcard0 and extsdcard. Which one is the actual SD card? Also where on the card should I place the videos? Ie: there's a downloads folder and dcim folder.

I'm trying to move some videos over to my SD card but there's 2 extensions for the SD card. Sdcard0 and extsdcard. Which one is the actual SD card? Also where on the card should I place the videos? Ie: there's a downloads folder and dcim folder.